It is well known that thin metallic and ceramic layers may be deposited upon a substrate by a technique known as "magnetron sputtering". By such methods, a metal layer may be sputtered in an argon atmosphere using a target of the material to be deposited, generally as a cathode in a standard RF sputtering apparatus.
More recently, sputtering techniques have been used in the production of integrated circuits which require rapid and economical metal deposition with very close tolerances. Sputtering is an especially useful tool for the application of films and coatings where uniformity and chemical purity is important. Manufacturing costs may be lowered by improving film uniformity and deposition rate in high speed production processes typically used in integrated circuit manufacturing. Materials of particular importance in the manufacture of integrated circuits are aluminum and aluminum alloys. Targets of aluminum and/or aluminum alloys are used for sputtering to produce an aluminum film or coating on a substrate.
Sputtering processes and apparatus are disclosed in Bergmann et al., U.S. Pat. Nos. 4,889,772 and 4,961,831; Shagun et al., U.S. Pat. No. 4,961,832; Shimamura et al., U.S. Pat. No. 4,963,239; Nobutani et al., U.S. Pat. No. 4,964,962; Arita, U.S. Pat. No. 4,964,968; Kusakabe et al., U.S. Pat. No. 4,964,969 and Hata, U.S. Pat. No. 4,971,674; and the references referred to therein; sputtering targets are discussed also in Fukasawa et al., U.S. Pat. Nos. 4,963,240 and 4,966,676; and Archut et al., U.S. Pat. No. 4,966,677. These disclosures of sputtering processes and apparatus as well as sputtering targets are expressly incorporated herein by reference.
The effect of crystallographic orientation of a sputtering target on sputtering deposition rate and film uniformity has been described in an article by C. E. Wickersham, Jr. entitled Crystallographic Target Effects in Magnetron Sputtering in the J.Vac. Sci. Technol. A5(4), July/August 1987 publication of the American Vacuum Society. In this article the author indicates that improvements in film uniformity may be achieved on a silicon wafer by controlling the working process for making a target so that an optimum crystallographic orientation is maintained in the target; however, target grain size is indicated as significantly less important. Specifically, aluminum alloy targets fabricated with different crystallographic orientations were examined and reported upon in the article. The crystallographic orientations were determined by X-ray diffraction pole figures.
Crystallographic orientation is also discussed in an article entitled Drift in Film Uniformity Arising from Sputtering Target Recrystallization by Haupt and C. E. Wickersham which appeared in the J. Vac.Sci.Technol A7 May/June 1989 publication of the American Vacuum Society. This article indicates that target recrystallization can be a significant source of thickness uniformity variation in sputtering operations but emphasizes the importance believed to be attributed to operating temperature of the target and the target recrystallization temperatures.
In an article entitled Aluminum Alloys for Present and Future Devices, by Daniel R. Marx published by the Materials Research Corporation (1990) aluminum alloys to be used in semiconductor devices are discussed and it is indicated that controlled thermomechanical processes can produce fine grained target structures but that the simple application of conventional hot working is accompanied by some undesirable effects which will tend to cause arcing during sputtering.
The disclosures of the foregoing articles are also expressly incorporated herein by reference.
The present invention provides an aluminum target suitable for magnetron sputtering which results in improved deposition rate and improved thickness uniformity of the coating or film applied to a substrate.